Increased spectral efficiency and reduced synchronization delay with bundled transmissions

ABSTRACT

Techniques are provided for increasing spectral efficiency over data channels in a storage or communication system. In some embodiments, data may be encoded and transmitted over multiple channels. The transmitted data from the multiple channels may be considered together as a channel bundle, thereby increasing the edge transitions of the group of signals to improve clock recovery and reduce coding constraints. In some embodiments, the channel bit size is reduced to maximize data rates based on the reduced coding constraints. Furthermore, the channel bundle has only one channel with timing markers, so that a receiver may receive information from the channel bundle and recover clocking based on the timing markers in the one channel.

BACKGROUND

The subject matter disclosed herein relates to optical systems, and moreparticularly, to techniques for transmitting data in optical systems.

Optical technologies have advanced along with the desire for greaterefficiency over optical channels. In particular, optical storagetechnologies and optical communication systems have been developed forincreased storage capacity and increased data rates.

One example of the developments in optical storage technologies may bethe progressively higher storage capacities for optical storage systems.For example, the compact disc, developed in the early 1980s, has acapacity of around 650-700 MB of data, or around 74-80 min. of a twochannel audio program. In comparison, the digital versatile disc (DVD)format, developed in the early 1990s, has a capacity of around 4.7 GB(single layer) or 8.5 GB (dual layer). Furthermore, even higher capacitystorage techniques have been developed to meet higher demands, such asthe demand for higher resolution video formats. For example,high-capacity recording formats, such as the Blu-ray Disc™ format, iscapable of holding about 25 GB in a single-layer disc, or 50 GB in adual-layer disk. As computing technologies continue to develop, storagemedia with even higher capacities may be desired. For example,holographic storage systems and micro-holographic storage systems areexamples of other developing storage technology that may achieve futurecapacity requirements in the storage industry.

Along with increases in data capacity, high data rates are also desired.For example, the video bit rate for a standard DVD format may be about9.8 Mbps, and the video bit rate for a standard Blu-ray Disc™ format maybe about 40.0 Mbps. Data rate increases may also be expected as highercapacity storage systems (e.g., holographic or micro-holographic storagesystems) are developed. Furthermore, increased data rates in opticalcommunications systems (e.g., transmittance of optical signals overfiber, water, free space, etc.) may also be desirable.

Data rates in optical systems may be at least partially limited by thespeed at which data may be transmitted. Methods for increasing theefficiency of data transmission over optical channels may improve datarates and/or accuracy in optical systems.

BRIEF DESCRIPTION

An embodiment of the present techniques provides a method oftransmitting optical data. The method involves transmitting data over achannel bundle having multiple optical channels, where the datatransmitted over the channel bundle is arranged to be decoded together.

Another embodiment provides a method of receiving optical data. Themethod includes receiving optical data from a channel bundle havingmultiple optical channels and recovering source data from the receivedoptical data using one decoder.

Another embodiment provides an optical system having an encoder system,a transmitter, a receiver system, and a decoder. The encoder system isconfigured to encode source data into optical data to be transmittedover a channel bundle having multiple optical channels. The transmitteris configured to transmit the optical data through the channel bundle.The receiver system is configured to receive the optical data from thechannel bundle, and only one decoder is configured to decode the opticaldata.

Yet another embodiment provides an optical storage system having one ormore encoders, an optical head, a multi-head detector, and clockrecovery circuitry. The one or more encoders encodes source data intooptical data to be recorded on multiple data tracks of an opticalstorage disk. The optical head is configured to impinge a beam on eachof the multiple data tracks to record the optical data in the multipledata tracks. The multi-head detector has multiple detector heads, whichare each configured to detect recorded data from each of the multipledata tracks. The clock recovery circuitry is configured to process therecorded data from each of the multiple data tracks together to recoverthe source data.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a block diagram of an optical storage system, in accordancewith embodiments;

FIG. 2 illustrates an optical disk having data tracks, in accordancewith embodiments;

FIG. 3 is a diagram representing channel bits in a minimum runlengthtime for Run-length Limited (RLL) encoded data;

FIG. 4 illustrates a group of signals from a channel bundle, inaccordance with embodiments;

FIG. 5 is a diagram representing channel bits having decreased channelbit size in a minimum runlength time for RLL encoded data, in accordancewith embodiments;

FIG. 6 illustrates timing markers in channel bundle, in accordance withembodiments;

FIG. 7 is a block diagram representing an encoding system using multipleencoders to output encoded data to a channel bundle, in accordance withembodiments;

FIG. 8 is a block diagram representing an encoding system using a commonencoder to output encoded data to a channel bundle, in accordance withembodiments; and

FIG. 9 is a block diagram representing a decoding system using amulti-head decoder and clock recovery circuitry to receive and clockdata from a channel bundle, in accordance with embodiments.

DETAILED DESCRIPTION

One or more embodiments of the present techniques will be describedbelow. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for one of ordinary skill having the benefit of thisdisclosure.

The present techniques disclose systems and methods for increasingspectral efficiency over channels in an optical system. An opticalsystem may include systems which transmit information using light (e.g.,a laser) as a medium, and may include, for example, optical storagesystems and optical communications systems. Optical channels may referto communication paths in an optical system, such as a path between anoptical disk and an optical head (e.g., a read/write head, a detector)in an optical storage system, or a path between a transmitter and areceiver in an optical communications system. Such channels may include,for example, fiber, water, or free space, etc. in different types ofoptical systems. Spectral efficiency may refer to the data rate orinformation rate of data transmittance over optical channels.

Optical systems typically involve encoding data to be transmitted asoptical data, and then receiving and decoding the data to obtaininformation corresponding to the original data source. For example, inoptical storage systems, data may be recorded or written to an opticaldisk by directing a recording beam and a reference beam from an opticalhead to a data position in the optical disk. The beams may interfere tomodulate the refractive index of the photosensitive material in theoptical disk to write data in the form of optical data (e.g., hologramsor micro-holograms). To retrieve the stored optical data, an opticalhead may direct a reading beam to the optical disk and receivetransmissions, reflections, and/or scatterings of the beam from theoptical data in the disk. The transmissions, reflections, and/orscatterings may be processed into a bit stream and decoded toreconstruct data corresponding to the originally encoded and recordeddata.

An example of an optical storage system is provided in FIG. 1. Anoptical storage system 10 may involve reading data from and/or recordingdata to optical storage disks 12. In one embodiment, the optical storagesystem 10 may be a holographic storage system, and the optical disk maybe a holographic disk 12. The data stored on the optical disk 12 may beread by a series of optical elements 14, which may be suitable foremitting beams 16 (e.g., a reading beam or a recording beam) andreceiving reflections 18 (e.g., including light scatter, reflection,and/or diffraction of the beams 16 by the medium of the disk 12) of thebeams from the optical disk 12. The optical elements 14 may include anynumber of different elements designed to generate excitation beams(e.g., lasers), or other elements such as an optical head configured tofocus the beams 16 on the optical disk 12 and/or detect the reflections18 coming back from the optical disk 12. The optical elements 14 arecontrolled through a coupling 20 to an optical drive electronics package22. The optical drive electronics package 22 may include such units aspower supplies for one or more laser systems, detection electronics todetect an electronic signal from the detector, analog-to-digitalconverters to convert the detected signal into a digital signal, andother units such as a bit predictor to predict when the detector signalis actually registering a bit value stored on the optical disk 12.

The location of the optical elements 14 over the optical disk 12 iscontrolled by servo-mechanical devices controlled by a processor 24. Insome embodiments in accordance with the present techniques, theprocessor 24 may be capable of determining the position of the opticalelements 14, based on sampling information which may be received by theoptical elements 14 and fed back to the processor 24. The processor 24also controls a motor controller 26 which provides the power 28 to aspindle motor 30. The spindle motor 30 is coupled to a spindle 32 thatcontrols the rotational speed of the optical disk 12. As the opticalelements 14 are moved from the outside edge of the optical disk 12closer to the spindle 32, the rotational speed of the optical disk maybe increased by the processor 24. This may be performed to keep the datarate of the data from the holographic storage disk 12 essentially thesame when the optical elements 14 are at the outer edge as when theoptical elements are at the inner edge.

The system 10 may be used to read an optical disk 12 containing data, asshown in FIG. 2. Generally, the optical disk 12 is a flat, round diskwith a recordable medium embedded in a transparent protective coating.The protective coating may be a transparent plastic, such aspolycarbonate, polyacrylate, and the like. A spindle hole 34 of the disk12 couples to the spindle (e.g., the spindle 32 of FIG. 1) to controlthe rotation speed of the disk 12. On each layer, data may be generallywritten in a sequential spiraling track 36 from the inner limit of thedisk 12 to an outer edge, although circular tracks, or otherconfigurations, may be used. The data layers may include any number ofsurfaces that may reflect light, such as micro-holograms which may beused for bit-wise holographic data storage, or a reflective surface withpits and lands.

It should be noted that while the example of an optical system asprovided in FIGS. 1 and 2 relate to optical storage (or holographicstorage), the present techniques of increasing spectral efficiency mayapply to any type of data storage or data transmission system. Forinstance, the present techniques may be implemented in data storagesystems such as magnetic storage systems and data transmission systemssuch as communication systems. In particular, the present techniques mayapply to any type of system which involves the transmitting andreceiving of data over a channel and/or over multiple channels (e.g., achannel bundle).

Typically, optical data may be encoded with Run-length Limited (RLL)codes. RLL codes may be suitable for optical systems, as information maybe encoded as optical data to be transmitted over optical channels.Typically, RLL codes constrain the intervals, also referred to as runs,of consecutive symbols (i.e., bits). More specifically, the shortest runof consecutive symbols (i.e., minimum runlength) is constrained suchthat short transmission symbols may be distinguishable. The longest runof consecutive symbols (i.e., maximum runlength) is constrained suchthat the transmitted signal may have enough signal transitions for clockrecovery. Therefore, channel bits are typically encoded to meet theconstraints of the shortest run constraint, typically denoted as d+1,and the longest run constraint, typically denoted as k+1.

A diagram representing encoded channel bits having a minimum runlengthof two (d=1) is provided in FIG. 3. The data stream 40 of FIG. 3 mayhave a minimum runlength of channel bits 44 (also referred to asconsecutive symbols 44) that is greater than or equal to the minimumtime 42. The minimum time 42, also referred to as the minimum runlengthtime 42, may be the length of time for transmitting the minimumrunlength of consecutive symbols 44. Coding techniques which constrainthe number of symbols 44 in a data stream 40 also limit the amount ofinformation communicated in transmitting the data stream 40. Forinstance, a sequence of r q-bit symbols may have less than q^(r) bits ofinformation, meaning the amount of information transmitted per channelbit 44 may be less than the size of each channel bit 44. Such acondition may indicate a failure to maximize spectral efficiency in theoptical channels. For example, a binary modulation using a (1,7) RLLcode relays approximately ⅔ of a bit of information per channel bit.

In one or more embodiments, multiple channels may be transmitted and/orreceived as a group to increase spectral efficiency. For example,signals from a group of multiple channels, referred to as a channelbundle, are illustrated in FIG. 4. The group of signals 46 may includemultiple signals 48 a-d, each from a different data channel in anoptical system. For example, in an optical storage system, each of thesignals 48 a-d may be from a different data track 36 on an optical disk12.

During a transmission of the group of signals 46, all of the signals 48a-d may be considered together as a group. Such a technique may bereferred to as channel bundling, and may be used to improvesynchronization time and clock recovery in comparison to typicaltechniques of considering one signal (e.g., 48 a) individually. A groupof signals 46 typically has a greater number of transitions from high tolow or from low to high (e.g., the rising edges 50 and falling edges 52)in comparison to an individual signal 48. The more frequent edgetransitions in the group of signals 46 may provide improved clockrecovery, thereby reducing the RLL coding constraint of the maximumrunlength for each individual data channel (e.g., the corresponding datachannels for each of the signals 48 a-d).

By using channel bundling to reduce the constraint of the maximumrunlength for each data channel, certain adjustments to the channel bitsize may be made to increase spectral efficiency. For example, in someembodiments, the size of each channel bit may be decreased. In someembodiments, the channel bit size may be decreased while the minimumrunlength is maintained to increase data rates (e.g., the informationtransmitted by a bit stream during the minimum runlength time). Forexample, the diagram illustrated in FIG. 5 represents a data stream 54having channel bits 56 with decreased size (e.g., in comparison to thechannel bits 44 of FIG. 3). The channel bits 56 illustrated in FIG. 5may be approximately half the size as the channel bits 44 illustrated inFIG. 3, such that during the minimum runlength time 42, approximately 4channel bits 56 may be transmitted, in comparison to the 2 channel bits44 transmitted when the channel bit size is not decreased.

In some embodiments, decreasing channel bit size in a data stream 54 mayimprove the information capacity of a data stream 54 within the boundsof the RLL code constraints, thereby improving spectral efficiency ofthe optical system. Even if a weaker code (e.g., one having a smallerinformation yield per bit) is used, the overall data rate may still beincreased. For example, assuming the code used for the data stream 40 ofFIG. 3 has two channel bits 44 in the minimum runlength time 42 and adata rate of 0.667 per channel bit 44, the information capacity of thedata stream 40 during time 42 may be approximately 1.33. Assuming thecode for the data stream 54 of FIG. 5 has 4 channel bits 56 in theminimum runlength time 42 and a data rate of 0.390 per channel bit 56(e.g., a weaker code than the one used for the bit stream 40 of FIG. 3),the information capacity of the data stream 54 during the time 42 may beapproximately 1.56. Therefore, even assuming a weaker code, thedecreased channel bit size of the channel bits 56 used in the datastream 54 may result in an increase (e.g., by approximately 17%) in datarate. Due to the increased signal transitions (e.g., edges 50 and 52from FIG. 4) when considering signals from a group of channels (e.g.,the group of signals 46), synchronization time may also be reduced.

Different channel bit lengths may also be used in different embodiments.For example, while the data stream 54 in FIG. 5 is illustrated as having4 channel bits 56 during the minimum runlength time 42, in differentembodiments, different numbers of channel bits may be transmitted duringa minimum runlength time 42. For example, channel bundling may be usedwith a data stream 40 having an unchanged channel bit size (e.g., thesame size of the channel bit 44), which may result in greater clockstability. In some embodiments, 3, 5, or more channel bits may betransmitted during a minimum runlength time 42. Furthermore, indifferent embodiments, decreasing channel bit size to increase thechannel bits transmitted in a bit stream may result in additionalchannel bits for coding gain. For example, channel codes using datarates of 8/9, 12/13, and 16/17 at the previously calculated 17% datarate increase may have resulting data rates of 1.04, 1.08, and 1.19(i.e., 1.17* 8/9, 1.17* 12/13, and 1.17* 16/17, respectively). Assuminga bit error rate (BER) of 1*10⁻⁴, using decreased channel bit size mayresult in gains of 3 to 4 data bytes for the 8/9 data rate code in someembodiments, or gains of 4 or 5 data bytes for different codes assuminga BER of 1*10⁻⁵.

The transmission and consideration of a group of signals from multiplechannels may also involve providing timing information. In someembodiments, timing markers may be positioned in intervals of selectdata channels during signal transmission of the channel bundle. Intypical data transmissions, encoding timing markers in a single channelmay be costly with respect to data rates and spectral efficiency, asadditional bit positions from each channel may be designated for timingmarkers to provide timing information. By encoding timing markers in asingle channel of a channel bundle, channel space may be preserved inthe remaining channels of the channel bundle, thereby reducing overhead.Furthermore, encoding timing markers on a single channel of a channelbundle may enable clock recovery of all signals from the channel bundle,based on the timing markers on the single channel.

FIG. 6 illustrates a channel bundle 58 having multiple channels 60 a-d,including one channel 60 b having encoded timing markers 62. Whiletiming information is provided by the timing markers 62 in the channel60 b, the remaining channels 60 a, 60 c, and 60 d of the channel bundle58 may not need to have timing markers. Therefore, the timing markers 62in one channel 60 b may provide timing information for the entirechannel bundle 58, and channel bit positions in the remaining channels60 a, 60 c, and 60 d need not be reserved for timing markers.

Transmission of multiple channels of optical data may involve differentencoding techniques. For example, in the block diagram of FIG. 7, inputs64 a, 64 b, and 64N may represent different portions of the informationto be separately encoded (blocks 66 a, 66 b, and 66N) and transmittedover channels 60 a, 60 b, and 60N of a channel bundle 58. As representedin FIG. 7, a channel bundle 58 may have N number of channels 60, and thetransmission of each channel 60 may involve the individual input andencoding of information to be transmitted through that channel 60. Thechannels 60 may be isolated by, for example, wavelength and/or spaceand/or polarization. For example, in an optical storage system, data maybe individually encoded (blocks 66 a, 66 b, and 66N) and recorded tospatially separate data tracks 36 in an optical disk 12. Furthermore, insome embodiments, multiple channel bundles 58 may be input, encoded, andrecorded simultaneously.

Another embodiment of an encoding system for channel bundling isprovided in FIG. 8, where one input 64 is encoded (block 66) andseparately processed (blocks 68 a, 68 b, and 68N) to be transmitted overdifferent channels 60 a, 60 b, and 60N. Therefore, information may beinput and encoded together before it is separated into differentchannels. As discussed, the channels 60 may be isolated by wavelengthand/or space and/or polarization. For example, in an optical storagesystem 10, different portions of the input 64 may be encoded (block 66)and separately processed to be recorded as multiple channels 60 a, 60 b,and 60N in one channel bundle 58. Each of the multiple channels 60 a, 60b, and 60N may be on separate data tracks 36 in an optical disk 12. Asdiscussed, more than one channel bundle 58 may be encoded, processed,and recorded simultaneously.

To receive information from the channel bundle 58, a receiver system mayreceive data from each of the parallel channels 60 and conduct parallelclock recovery and synchronization on the data from the parallelchannels. FIG. 9 illustrates a receiver system 70 having separatereceivers 72 for receiving data from each channel 60. For instance, datafrom channel 60 a may be received at receiver 72 a, data from channel 60b may be received at receiver 72 b, and so forth. Once the data from thechannel bundle 58 is received at the receiver system 70, the data may beprocessed at a clock recovery circuit 74 for clock and data recovery.For example, in an optical storage system 10, the receiver system 70 maybe a multi-head detector 70 (e.g., part of the optical elements 14) andmay have multiple detector heads 72 each suitable for detectingreflections, scatterings, and/or diffractions of optical data from anoptical disk 12. The multi-head detector 70 may transmit the data fromchannel bundle 58 to the clock recovery circuitry 74 which may be, forexample, a digital signal processor (e.g., processor 24) or anapplication-specific integrated circuit in the optical storage system10. While detected signals may be processed separately for clock anddata recovery in typical systems, in accordance with the presenttechniques, substantially all the data detected at the multi-headdetector 70 may be considered together (i.e., in parallel) at the clockrecovery circuitry 74 for clock and data recovery. In some embodiments,the clock recovery circuitry 74 may be suitable for parallel clockrecovery and synchronization. For example, in some embodiments, theclock recovery circuitry 74 may have one or more microprocessors orcontrollers recovering clock information of the data in parallel.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A method of communicating data, the method comprising: transmittingdata over a channel bundle comprising multiple channels, wherein thedata transmitted over the channel bundle is arranged to be decodedtogether.
 2. The method of claim 1, comprising: encoding data using arun-length limited (RLL) encoding scheme, wherein the data is encoded tomeet a minimum runlength constraint of the RLL encoding scheme.
 3. Themethod of claim 2, wherein the data is encoded to meet a maximumrunlength constraint.
 4. The method of claim 1, wherein transmitting thedata over a data bundle comprises: encoding the data to be recorded tomultiple data tracks of a holographic disk, wherein each of the multipledata tracks corresponds with one of the multiple channels.
 5. The methodof claim 4, wherein encoding the data to be recorded to the multipledata tracks comprises separately encoding multiple data streams, whereineach of the multiple data streams is to be recorded to one of themultiple data tracks.
 6. The method of claim 4, wherein encoding thedata to be recorded to the multiple data tracks comprises: encoding thedata to produce one encoded data stream; and processing the one encodeddata stream into multiple data streams, wherein each of the multipledata streams is to be recorded to one of the multiple data tracks. 7.The method of claim 1, comprising: receiving the data from the channelbundle; and recovering clock information for the data from the channelbundle.
 8. The method of claim 7, wherein receiving the data from thechannel bundle comprises detecting data from multiple data tracks of aholographic disk, wherein each of the multiple data tracks correspondswith one of the multiple channels.
 9. The method of claim 8, whereinrecovering clock information comprises recovering clock information ofthe data from the multiple channels substantially in parallel.
 10. Themethod of claim 8, wherein clock information of the data from each ofthe multiple channels of the channel bundle is recovered substantiallyin parallel by clock recovery circuitry.
 11. A method of communicatingdata, the method comprising: receiving data from a channel bundlecomprising multiple channels; and recovering source data from thereceived data using one decoder.
 12. The method of claim 11, comprising:encoding source data to be transmitted in the channel bundle; andproviding timing information in the first optical channel.
 13. Anoptical system, comprising: an encoder system configured to encodesource data into encoded data to be transmitted over a channel bundlecomprising multiple channels; a transmitter configured to transmit theencoded data through the channel bundle; a receiver system configured toreceive the encoded data from the channel bundle; and only one decoderconfigured to decode the encoded data into source data.
 14. The opticalsystem of claim 13, wherein the encoder system is configured to encodethe source data into encoded data using a run-length limited (RLL) code.15. The optical system of claim 13, wherein the encoder system isconfigured to constrain the encoded optical data by a minimum runlengthconstraint.
 16. The optical system of claim 13, wherein the encodersystem comprises multiple encoders, each configured to encode a portionof the source data into a portion of the encoded data.
 17. The opticalsystem of claim 13, wherein the receiver system comprises multiplereceivers, each configured to receive a portion of the encoded data fromone of the multiple channels.
 18. The optical system of claim 13,wherein the decoder is configured to decode the data from each of themultiple channels substantially simultaneously.
 19. The optical systemof claim 13, wherein the multiple channels are separated by one or moreof space, wavelength, and polarization.
 20. The optical system of claim13, comprising an optical disk comprising the channel bundle. 21.-23.(canceled)
 24. An optical storage system comprising a channel bundlecomprising multiple optical channels, wherein data transmitted throughthe multiple optical channels of the channel bundle is received at onlyone decoder configured to decode the transmitted data.
 25. The opticalstorage system of claim 24, comprising an optical disk comprising one ormore channel bundles.